Would your keel joint survive a full speed impact? - SailNet Community
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post #1 of 37 Old 01-02-2012 Thread Starter
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Would your keel joint survive a full speed impact?

I am wondering how many of us with fins bolted on feel the hull we have could survive a full force impact with something fixed.

I have no obvious signs of failure at the keel stub joint on TD. It is a 1976 Islander 28. No leaks. The visible bolts are badly rusted to the ss nuts. Outside, I can see the seam between lead and fg in places when is is on the hard and gets wet. There is no visible gap but a line appears as rainwater runs along it.

The boat is doing its job well and we would like to head a little further afield. As we study the safety of "real" cruising boats with encapsulated keels or thick aluminum hulls it makes me pause to think what I would be doing on TD immediately after hitting something fixed at speed. Would I be plugging leaks or would I have lost the keel? Is this an acceptable risk?

Would your fin survive a full speed impact?

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post #2 of 37 Old 01-02-2012
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Define "survive".....

Few boats would suffer leakage immediately, I suspect, but the amount of damage inflicted will vary substantially depending on a number of factors. One of the largest factors will be keel material. Lead absorbs an amazing amount of energy as it deforms under impact. Iron keels do not and transfer the full forces to the hull - therefore internal damage is likely to be more significant with iron keels.

Most hulls can absorb the flexing that results with the leverage of the keel applies the rotating forces of impact into the hull. The area immediately aft of the keel is usually more affected, as the keel tries to rotate into the hull there. Solid glass hulls may flex and absorb the brunt of the impact, but generally any tabbed stringers and floors are likely to be separated from the hull, reducing structural integrity there. In extreme cases the laminate may be fractured in a way that can be difficult to determine. On a lightly built boat I suppose the narrow, pointed aft section of the keel might actually puncture the hull.... that would, of course, be bad news....

With cored hulls and their inherent stiffness, if their strength is overcome in impact then there may be delamination of the core and skins in that area as well as tabbing separation - leading to a bigger repair job. But even cored hulls are generally solid glass in that area...

The nasty part of all this is that often the damage, even if considerable, will not be particularly visible.. esp in the presence of extensive liner use. btw if you see a new crack in a liner then it's almost certain there's more/worse underneath.

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".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)

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post #3 of 37 Old 01-02-2012
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Catalina 27' hit pretty hard going maybe 5 knots. As Faster said the keel was rotated up and aft of the keel was damaged. It was taking on water but very slowly, maybe a cup a day. Had insurance repair it.
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post #4 of 37 Old 01-02-2012
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The joint and bolts were OK but about two feet BEHIND the keel the hull suffered pretty badly and leaked a good bit till we took down the sails and backed off the rigging


It took a rather large truckload of money as 7' keels seem to be quite the lever

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post #5 of 37 Old 01-02-2012
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Yes - properly done these kinds of repairs can quickly run into 5 digits...

btw Tommays, that's no stock C&C... do you know who did the keel??

Ron

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".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
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post #6 of 37 Old 01-02-2012
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Two different casesfor cast iron keels:

1. The boat hit rocks with speed of 5 knots. The keel was not damaged but the hull was broken at the aft end of the keel. They managed to get to the marina which was very near and immediately taken to dry land.

2. The boat hit rocks exceeding 6 knots. Ribs and leg bones of different crews were broken due to immediate stopping of the boat. No water inside the hull and no damage to the hull. They sailed approximately for 50 miles. Only the front part of the keel was broken. The keel only lost 15 -20 lbs of metal from the front part.

The answer is "it depends".
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post #7 of 37 Old 01-02-2012
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The orginal owner had a few dollars to throw around and spent them on the boat and then went to the next stage and hired Britton Chance who did TWO keels(he did not like the first one ) a rudder and the current double spreader rig

At some point he moved on and it fell into a sad state and my friend brought it back to life


The boat has a PHRF of 117 compared to the stock 35 and is still competive if we point the right way

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post #8 of 37 Old 01-02-2012 Thread Starter
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I am encouraged! Ha!

"Survive", as in make it to a port.

The only time I have hit anything with the keel was loading it onto a truck at haul out. I bumped the wooden cross beam / keel support as I approached the Brownell trailer. The trailer was not deep enough. I was barely moving and the jolt gave me pause. It is a 3000 lb. chunk of lead bolted to about 4000 lbs of boat and it came to a sudden stop! There was a little momentum involved but no opportunity for a rotational moment as the trailer's pads were high enough to brace the hull. It made me wonder what would happen if we really smacked something motoring into an unfamiliar cove in Newfoundland.

Thanks for all the good information.

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post #9 of 37 Old 01-02-2012
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As has been said, very few boats can withstand a full speed collision with an immovable object such as a rock. I apologize that I had written this for an earlier discussion on this topic and so it may not be completely relevant.

With a bolt-on keel, the good news is that if the boat does not sink, a nearly good as new repair can usually be made. The bad news is that this can often involve removing the keel, cutting away all damaged glass (which may include the internal framing as well, doing a careful rebuild. It is rare that the bolts themselves fail and when they do, it is usually a case where corrosion has badly reduced the diameter of the bolt.

Lead keels are generally considered better the cast iron in these types of collisions because the lead can absorb some of the shock and therefore impart less force into the hull and keel attachment structure.

This kind of full speed impact with the proverbial immovable object is especially devastating to most encapsulated keels. In a full speed collision, the fiberglass itself comes into contact with the object and is generally crushed and deformed. This allows the ballast keel to be pushed upward into the bilge membrane. Unlike most bolt on keels, encapsulated keels rarely have the internal structure to absorb and distribute these impact forces.

Successfully rebuilding this kind of damage is much more difficult. The ballast should be removed, the encapsulation envelope checked for internal damage, and repaired, the ballast bonded back in place, and the internal bilge membrane rebuilt. It is very hard to get this back to being a like-new repair.

Owners and insurance companies often elect to merely repair the point of contact on the encapsulation envelope. That often is not an adequate repair. The bond between the ballast keel and the keel envelope, is a part of the structure of the boat. It allows the load of the ballast to transfer and be distributed into the hull, and is the reason that encapsulated keels often get by with minimal internal framing. In the kind of grounding being discussed, that bond between ballast keel and the shell is generally broken resulting in a boat with substantially less resistance to the next hard grounding, with a greater tendency for blisters due to moisture trapped in the encapsulation, and greater tendency toward flexure and therefore fatigue.
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Quote:
Originally Posted by Jeff_H View Post

Owners and insurance companies often elect to merely repair the point of contact on the encapsulation envelope. That often is not an adequate repair. The bond between the ballast keel and the keel envelope, is a part of the structure of the boat. It allows the load of the ballast to transfer and be distributed into the hull, and is the reason that encapsulated keels often get by with minimal internal framing. In the kind of grounding being discussed, that bond between ballast keel and the shell is generally broken resulting in a boat with substantially less resistance to the next hard grounding, with a greater tendency for blisters due to moisture trapped in the encapsulation, and greater tendency toward flexure and therefore fatigue.
this is very scary. How do you survey for this, or do you just pass on all encapsulated keels?
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